Numerous heating devices, typically electrical and battery-powered, are known for heating ski boots and work boots to provide comfort to the wearer, who is required or desires to be out of doors in cold weather for an extended period of time. While these devices have been known for many years, many have significant drawbacks and disadvantages. For example, some of these devices do not distribute the heat evenly, resulting in hot spots which may damage the wearer's skin. In addition, many of these devices do not provide a substantially continuous flow of heat, and therefore, the wearer's feet periodically experience coldness or discomfort. Moreover, these devices tend not to provide any heat storage capacity and thereby require extensive battery use which quickly drains the batteries. Finally, many of these prior devices are relatively bulky and complicated and costly to make, are not sufficiently flexible, and are not sufficiently corrosion proof when exposed to human perspiration.
Examples of these prior devices are disclosed in the following U.S. Pat. Nos.: 2,298,299 to Joy et al; 3,293,405 to Costanzo; 3,663,796 to Hines et al; 3,906,185 to Gross et al; 3,946,193 to Giese; 4,080,971 to Leeper; and 4,665,301 to Bondy; and in Austrian patent 383,478B to Macher and Zorn, and German patent 386830, the disclosures of which are hereby incorporated herein by reference.